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Thursday, December 18, 2014

White Fuzzies on Cactus Probably Cochineal Scale

Q. I planted a "cows tongue" or sometimes called "angel wing" cactus last spring and over the summer it began to develop some white cottony looking growth around each of the spines on the lower pads.  The white growth has continued and now covers much of the pads and some of the lower pads have actually fallen off. What is this white growth?  Is this a common problem with the cows tongue or is it common to all padded cacti and if so what can be done to rid the plant of the growth.  Someone had mentioned that it could be because of my watering schedule.  What do you think?
A. I don't have a picture of this problem on your cactus so I am following the KISS (Keep It Simple Stupid) diagnosis technique. The stupid part is to remind me that nine times out of 10 it is a common problem, not a rare event.

This is most likely problem is Cochineal scale, a common problems on cacti.
Heavy infestation of cochineal scale on Opuntia cactus.
If you touch it and it leaves a blood red liquid on your finger it is Cochineal scale. Both are scale insects hiding under that cottony growth and feeding on plant juices. When they reproduce and their populations increase, the feeding damage is so great it causes the plant or parts of the plant to collapse and ultimately die.
The red dye produced by cochineal scale when it is damaged. Notice how cochineal scale is commonly found close to the spines.
For either of these insects the control measures are the same. You can take a cotton swab and dab each of the cottony growths with alcohol or apply a systemic insecticide to the soil such as those containing imidicloprid so the poison will be taken up by the roots and moved to where this scale insect is feeding thus killing the insect.

The cochineal scale has an interesting history in Central America where this red extract was valued by Spanish colonizers as a dye until it was replaced by synthetic dyes. The actual insect was a very close relative of the Cochineal scale we see in our landscapes now. 

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